From 0112e4292e5293c6211471a131552469ad6f9595 Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Tue, 4 Feb 2025 11:17:44 -0800
Subject: [PATCH] ICU-22962 Fix int32_t overflow issue when month is large

---
 icu4c/source/i18n/calendar.cpp         |  7 ++++++-
 icu4c/source/test/intltest/caltest.cpp | 16 ++++++++++++++++
 icu4c/source/test/intltest/caltest.h   |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/icu4c/source/i18n/calendar.cpp b/icu4c/source/i18n/calendar.cpp
index 167d8644827..d023b096d3a 100644
--- a/icu4c/source/i18n/calendar.cpp
+++ b/icu4c/source/i18n/calendar.cpp
@@ -3804,7 +3804,12 @@ int32_t Calendar::handleGetExtendedYearFromWeekFields(int32_t yearWoy, int32_t w
 
 int32_t Calendar::handleGetMonthLength(int32_t extendedYear, int32_t month, UErrorCode& status) const
 {
-    return handleComputeMonthStart(extendedYear, month+1, true, status) -
+    int32_t nextMonth;
+    if (uprv_add32_overflow(month, 1, &nextMonth)) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return 0;
+    }
+    return handleComputeMonthStart(extendedYear, nextMonth, true, status) -
         handleComputeMonthStart(extendedYear, month, true, status);
 }
 
diff --git a/icu4c/source/test/intltest/caltest.cpp b/icu4c/source/test/intltest/caltest.cpp
index d5a824ec6fa..90d3dba2eb4 100644
--- a/icu4c/source/test/intltest/caltest.cpp
+++ b/icu4c/source/test/intltest/caltest.cpp
@@ -217,6 +217,7 @@ void CalendarTest::runIndexedTest( int32_t index, UBool exec, const char* &name,
     TESTCASE_AUTO(Test22750Roll);
 
     TESTCASE_AUTO(TestChineseCalendarComputeMonthStart);
+    TESTCASE_AUTO(Test22962MonthAddOneOverflow);
 
     TESTCASE_AUTO_END;
 }
@@ -6004,6 +6005,21 @@ void CalendarTest::TestAddOverflow() {
     }
 }
 
+void CalendarTest::Test22962MonthAddOneOverflow() {
+    Locale locale("ckb_IQ@calendar=ethiopic-amete-alem");
+    UErrorCode status = U_ZERO_ERROR;
+    LocalPointer<Calendar> cal(Calendar::createInstance(
+            *TimeZone::getGMT(), locale, status));
+    cal->clear();
+    status = U_ZERO_ERROR;
+    cal->fieldDifference(
+        (double)115177509667085876226560460721710683457425563915331054206329829993967720136006086546037257220523631494518538798239249720325557586193565921621016454170342731307548672.0,
+        UCAL_MONTH, status);
+    status = U_ZERO_ERROR;
+    cal->set(UCAL_DAY_OF_WEEK_IN_MONTH , -2111799174);
+    cal->add(UCAL_ERA, -1426056846, status);
+    assertTrue("Should return failure", U_FAILURE(status));
+}
 void CalendarTest::Test22750Roll() {
     UErrorCode status = U_ZERO_ERROR;
     Locale l(Locale::getRoot());
diff --git a/icu4c/source/test/intltest/caltest.h b/icu4c/source/test/intltest/caltest.h
index e1a505292e5..c75b73464a0 100644
--- a/icu4c/source/test/intltest/caltest.h
+++ b/icu4c/source/test/intltest/caltest.h
@@ -352,6 +352,7 @@ public: // package
     void Test22730JapaneseOverflow();
     void Test22730CopticOverflow();
     void Test22962ComputeJulianDayOverflow();
+    void Test22962MonthAddOneOverflow();
 
     void Test22750Roll();